The abuse of designer drugs that act on biogenic amine receptors is a very serious ongoing problem worldwide. It is becoming epidemic with the influx of many novel substances largely produced by Asian criminal groups in attempts to circumvent drug laws. These drugs are not initially controlled by the authorities but are very close analogs of active compounds. Most such analogs have similar but not identical activity to the parent substances and frequently produce dangerous and unpredictable effects. The recent appearance of methylenedioxypyrovalerone (MDPV) and flakka (alpha-pyrrolidinopentiophenone) referred to as bath salts are glaring examples of such highly problematic drugs. Recent work has shown that methamphetamine (METH) and 3,4-methylenedioxy-methamphetamine (MDMA) adversely affect the integrity of the blood-brain barrier (BBB) however, there are no current reports on the effects of MDPV on the BBB. We compared the effects of METH, MDMA and MDPV on bovine brain microvessel endothelial cells (bBMVECs), an accepted in vitro model of the BBB in order to gain further insight into the toxicity of these drugs. Confluent bBMVEC monolayers were treated with METH, MDMA and MDPV (0.5mM-2.5mM) for 24h. METH and MDMA increased lactate dehydrogenase release only at the highest concentration (2.5mM), whereas MDPV induced cytotoxicity at all concentrations. MDMA and METH decreased cellular proliferation only at 2.5mM, with similar effects observed after MDPV exposures starting at 1mM. Only MDPV increased reactive oxygen species production at all concentrations tested whereas all 3 drugs increased nitric oxide production. Morphological analysis revealed different patterns of compound-induced cell damage. METH induced vacuole formation at 1mM and disruption of the monolayer at 2.5mM. MDMA induced disruption of the endothelial monolayer from 1mM without vacuolization. On the other hand, MDPV induced monolayer disruption at doses0.5mM without vacuole formation; at 2.5mM, the few remaining cells lacked endothelial morphology. Our data suggest that even though these synthetic psychostimulants alter monoaminergic systems, they each induce BBB toxicity by different mechanisms with MDPV being the most toxic.